1. Field of Invention
The present invention relates generally to the fields of oilfield exploration, production, and testing, and more specifically to methods and apparatus for controlling the rates of swelling of elastomeric materials that may be used as packers, seals or the like.
2. Background
Swellable polymers for use in packers have received considerable attention. U.S. Pat. No. 2,849,070, issued to George Maly in 1958, was the first patent to disclose swell packers. EP1672166A1 discloses packers having a swellable core surrounded by a coating. This patent explains that the rubber of the core can have other materials dissolved therein or may be a mixture containing fibers or cellulose. Another option disclosed in this EP patent is rubber in mechanical mixture with other polymer that expands upon contacted with oils. The coating has a higher resistance to the fluid and lower rates of diffusion for the fluid than the core. Thus, the coating disclosed in EP1672166A1 retards the rates of swelling and therefore can provide a delay in the swelling of the core, preventing the core from premature swelling. However, this same property of the coating also leads to longer times for the cores to expand and for the packers to set and seal.
To overcome some of the problems with the longer times needed to expand the packers, EP1672166A1 discloses an impermeable coating with small portions of the cores exposed. While this approach alleviates some of the problems associated with completely impermeable coatings, leaving a small region of core exposed still does not allow the unexposed regions to swell at a high rate.
U.S. application Ser. No. 11/769,207 discloses temporary containments for swellable packer elements. This application discloses methods for creating temporary containments by using sleeves made of materials that are soluble in specific activation fluids. The dissolvable protective sleeves can prevent the premature and undesired swelling of the packers. When it is desired to expand the packer, the temporary containments are dissolved (e.g., by introducing an activation fluid) to allow the swellable polymers in the cores to contact the fluids to allow the packers to expand.
In a similar approach, U.S. Patent Application Publication No. 20060185849 discloses a device which consists of a swellable elastomer core with a protective layer for fluid control. The protective layers may be removed by mechanisms, such as temperature, chemicals, radiation (magnetic transmission, electromagnetic transmission, or heat) or mechanical techniques.
Some protective layers may be removed with specific chemicals. For example, U.S. Patent Application Publication No. 20050199401 discloses devices with protective coatings that may be disintegrated by selected chemicals. These selected chemicals can be introduced into the well bore in the form of a pill or through a control line.
U.S. Patent Application Publication No. 20070027245 discloses water and oil swellable materials where the elastomers and non-elastomers may be layered, wherein individual layers may be the same or different in composition and thickness, interpenetrating networks, and the like.
Several other patents and applications also disclose swellable materials, including U.S. Pat. No. 7,059,415; WO 2005/012686, WO 2005/090741, WO 2005/090743, WO 2006/003112, WO 2006/003113, WO 2006/053896, EP 1407113, EP 283090, EP 1649136, U.S. Patent Application Publication No. 20070056735, WO 2006/063988, WO 2006/065144, WO 2006/121340, WO 2002/020941, WO 2005/116394, WO 2006/043829, and WO 2006/118470.
While these prior art technologies provide methods to delay and control the timing and rates of swellable packer expansion, there is still a need for better methods and devices for controlling the deployment and setting of swellable packers or similar devices downhole.